ENVIRONMENTAL LEGACY OF COAL COMBUSTION: WIDESPREAD CONTAMINATION OF LAKE SEDIMENTS AND CHRONIC RISKS TO AQUATIC ECOSYSTEMS

Coal ash is generated from coal combustion for electricity and represents one of the largest industrial solid waste streams in the United States. A significant amount of coal ash is disposed of in surface impoundments and landfills, many of which are adjacent to natural waterways used for turbine cooling in coal-fired power plants. Previous catastrophic and chronic releases of coal ash to the environment have raised wide public concerns about the potential risks posed to both human and ecological health. While the impacts of released coal ash on water resources have been addressed extensively, the influences on the quality of aquatic sediment and the associated potential ecological risks have been largely overlooked.

Here we show widespread coal ash contamination, both temporally and spatially, in ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores and surface sediments retrieved from lakes near coal-fired power plants across North Carolina. Toxic trace elements typically enriched in coal ash, including As, Se, Mo, Cd, Sb, Tl, and Pb, were elevated in sediments collected downstream from the coal ash ponds above upstream reference sediments. Similarly, strontium isotope ratios of downstream sediments exhibited a close resemblance to coal fly ash and were distinctive from upstream reference sediments. In addition to the geochemical data, fine-grained spherical and amorphous coal ash particles were physically detected in sediments with optical and scanning electron microscopy and magnetic susceptibility was also above background measurements. The concentrations of trace element contaminants within sediment exceeded the census-based sediment quality guideline values, which indicates significant risks to the ecological health of sediment-dwelling and other aquatic organisms and eventually could lead to bioaccumulation. Meanwhile, many of the contaminants showed mobilization from sediment to ambient porewater, which could further increase their potential for bioavailability. Given that there are hundreds of coal ash disposal units in close proximity to aquatic systems across the U.S., we assert that sediment contamination is more common than previously thought and associated ecological risks are prevalent nationwide and globally where coal combustion is a dominant energy source.